The effect of acoustically-induced cavitation on the permeance of a bullfrog urinary bladder.

It is well known that ultrasound enhances drug delivery to tissues, although there is not a general consensus about the responsible mechanisms. However, it is known that the most important factor associated with ultrasonically-enhanced drug permeance through tissues is cavitation. Here we report results from research conducted using a experimental approach adapted from single bubble sonoluminescence experiments which generates very well defined acoustic fields and allows controlled activation and location of cavitation. The experimental design requires that a biological tissue be immersed inside a highly degassed liquid media to avoid random bubble nucleation. Therefore, live frog bladders were used as the living tissue due to their high resistance to hypoxia. Tissue membrane permeance was measured using radiolabeled urea. The results show that an increase in tissue permeance only occurs when cavitation is present near the tissue membrane. Moreover, confocal microscopy shows a direct correlation between permeance increases and physical damage to the tissue.

Preliminary evidence for a change in spectral sensitivity of the circadian system at night.

BACKGROUND: It is well established that the absolute sensitivity of the suprachiasmatic nucleus to photic stimulation received through the retino-hypothalamic tract changes throughout the 24-hour day. It is also believed that a combination of classical photoreceptors (rods and cones) and melanopsin-containing retinal ganglion cells participate in circadian phototransduction, with a spectral sensitivity peaking between 440 and 500 nm. It is still unknown, however, whether the spectral sensitivity of the circadian system also changes throughout the solar day. Reported here is a new study that was designed to determine whether the spectral sensitivity of the circadian retinal phototransduction mechanism, measured through melatonin suppression and iris constriction, varies at night. METHODS: Human adult males were exposed to a high-pressure mercury lamp [450 lux (170 microW/cm2) at the cornea] and an array of blue light emitting diodes [18 lux (29 microW/cm2) at the cornea] during two nighttime experimental sessions. Both melatonin suppression and iris constriction were measured during and after a one-hour light exposure just after midnight and just before dawn. RESULTS: An increase in the percentage of melatonin suppression and an increase in pupil constriction for the mercury source relative to the blue light source at night were found, suggesting a temporal change in the contribution of photoreceptor mechanisms leading to melatonin suppression and, possibly, iris constriction by light in humans. CONCLUSION: The preliminary data presented here suggest a change in the spectral sensitivity of circadian phototransduction mechanisms at two different times of the night. These findings are hypothesized to be the result of a change in the sensitivity of the melanopsin-expressing retinal ganglion cells to light during the night.

Additivity in murine circadian phototransduction.

Additivity in the circadian phototransduction system of the mouse has not been tested directly. Because of this, accurate prediction of circadian phase shifts elicited by polychromatic light stimuli cannot be derived from the results of studies using monochromatic light stimuli. This limitation also makes it impossible to deduce the relative contributions of the photoreceptive mechanisms (rods, cones and melanopsin-containing retinal ganglion cells) underlying circadian phototransduction in the mouse. Using nearly monochromatic light stimuli of different spectral composition, and combinations thereof, we demonstrated that murine circadian phototransduction exhibits additivity. Based on the locomotor activity phase shifts elicited by these stimuli, we developed the first quantitative assessment of the relative contributions of conventional and novel photoreceptive mechanisms for circadian functioning in the mouse.

Preliminary evidence for spectral opponency in the suppression of melatonin by light in humans.

Human adult males were exposed to light from blue light emitting diodes (18 lux; 29 microW/cm) and from clear mercury vapor lamps (450 lux; 170 microW/cm) during night-time experimental sessions. Both conditions suppressed nocturnal melatonin concentrations in blood plasma with the blue light more effective than mercury at melatonin suppression. No additive model incorporating opsin photopigments either alone or in combination could explain the results, but a model incorporating an opponent mechanism was consistent with the present data as well as data from previously published studies.

Effects of nitric oxide and angiotensin II and their interaction on water uptake in Rana catesbeiana.

Nitric oxide and angiotensin II are involved in regulation of water uptake at the pelvic patch of empty-bladder Rana catesbeiana. In whole animal studies, inhibition of nitric oxide synthase decreased water uptake by 25% and decreased the sodium content of skin from the pelvic patch region by 30%. The inhibitor of nitric oxide synthase also had no effects on permeability of isolated, unperfused skin from the pelvic patch region. These studies indicate that nitric oxide is regulating tissue salt concentration. Injection of angiotensin II stimulated water uptake at the pelvic patch by 23%, which was correlated with an increase in both the vascular resistance and the mean arterial pressure in the sciatic artery. Inhibition of nitric oxide synthase enhanced angiotensin II constriction of aortic rings from frogs. However, in the whole animal studies, inhibition of nitric oxide synthase before angiotensin II injection did not enhance water uptake as predicted. It is hypothesized that the pre-capillary bed of the pelvic patch in Rana catesbeiana lacks angiotensin II receptors.